¥Agronomia vol. 6 n. 2 July

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120 Baldini et al. Recent studies have verified the antioxidant properties of oleic acid (Berry and Rivlin, 1997) and have demonstrated that an increase in the oleic acid content in the tissues, in situations of high oxygen stress (oxygen toxicity), can contribute towards forming better cellular protection than a similar increase in polyunsaturated fatty acids (Kinter et al., 1996). Other studies done on the Chinese population in Hawaii have highlighted an inverse relationship between the consumption of monounsaturated fatty acids and cancer of the colon (Po Huang et al., 1996). For some years research has been underway with the aim of obtaining new high oleic varieties of sunflower, which has thoroughly tackled the problems related to the genetic control of high oleic acid content (Miller et al., 1987; Alonso, 1988; Fernandez-Martinez et al., 1989), lipid biosynthesis in both standard genotypes and those with a high oleic acid content in the achenes (Ohlrogge et al., 1991; Ohlrogge and Browse, 1995) and the effect of the main environmental factors (temperature in particular) that can modify the linoleic/oleic acid ratio in the oils (Harris et al., 1978; Goyne et al., 1979) due to the well-known affect on enzyme activity (oleoyl phosphatidylcholine desaturase or ∆ -12 desaturase) that converts oleic acid into linoleic acid (Garces et al., Garces and Mancha, 1989, 1001). Little has been done to study the effects of other agronomic factors on the fatty acid composition. In particular, the effect of water availability is more or less unknown, except for the study by Talha and Osman (1975) carried out before the existence of high oleic hybrids. This research studied the effect of water availability on fatty acid accumulation and final fatty acid composition in the oil in high oleic and standard hybrids. MATERIALS AND METHODS Two trials were done in 1997 and 1998 at the Experimental Farm of Udine University (46° 02’ N, 13° 13’ E and 110 m a.s.l.), using two different lysimeter systems. In 1997 12 underground lysimeters were used (length 1.1 m, width 0.8 m and depth 0.70 m). The lysimeters were filled with loam soil (20, 42 and 38% of clay, silt and sand, respectively) (0.5 m layer) and with sand, gravel and fine pebbles (0.2 m layer) for drainage and were protected from the rain by a transparent fixed canopy. In 1998 larger lysimeters were used (1.5 × 1.5 × 1.5 m), containing the same soil and protected from the rain by a mobile canopy on rails (12 lysimeters of which 2 were weighing, 4 with automatic regulation of water table depth and 6 drainage ones). The main climatic characteristics, divided into the pre- and post-flowering stages of the crop, were recorded at an automatic weather station close to the experiment (Table 1). As regards the water regimes reported in Table 2, it should be specified that the water table, where in<strong>vol</strong>ved, was maintained through hypogeal water refills at a constant depth of 0.5 m in the first year and 0.6 m in the second; that 60% and 100% ET represent the percentages of restoration of evapotranspiration (ETM) by means of hypogeal irrigation, in the first and second year, respectively, and that stress means no water restoration from flowering to physiological maturity. The field capacity (-0.02 MPa) and wilting point (-1.5 MPa) of the soil were measured in the laboratory as being 30 and 15% of soil <strong>vol</strong>ume, respectively. The soil water content in each lysimeter was measured every 3 days by TDR (Tektronics 1502C) using probes inserted at 20 and 40 cm depths and by oven-drying soil samples from the same depths every 15 days. The infor- Table 1. Weather conditions during the experiments. Average values of minimum temperature (Min T), maximum temperature (Max T), relative humidity (RU), solar radiation (Radiation) and rainfall (Rainfall) during sowing – end of flowering and end of flowering – physiological maturity periods. * Rainfall has not affected the trials Year Period Min T Max T RU Radiation Rainfall (°C) (°C) (%) (MJ m -2 day -1 ) (mm) * 1997 Sowing (04/04) – end flowering (06/07) 11.1 20.7 64.6 19.4 469 End flowering – physiol. maturity (06/08) 15.1 26.2 70.8 22.0 105 1998 Sowing (06/05)- end flowering (28/07) 12.4 25.3 68.6 21.7 265 End flowering – physiol. maturity (30/8) 17.3 29.3 65.2 21.1 91
mation obtained from the TDR probes, placed on all the lysimeters, was integrated with the values obtained from the two weighing lysimeters to identify when to irrigate. Two sunflower hybrids were used, one with a high oleic content (UD12) and the other a standard one (UD87), both characterised by the same crop cycle and selected by the Crop Production Department at the University of Udine (in the first year only the high oleic hybrid was used). Sowing was done on 04/04/1997 and 02/04/1998; after thinning 6 plants m -2 remained (6 plants per lysimeter in 1997 and 15 per lysimeter in 1998). Base fertilisation was done with 150 kg of P 2 O 5 and 200 kg of K 2 O. At the B6 stage (Merrien, 1986), a side dressing was done with approx. 120 kg of N in the form of ammonium nitrate. Two treatments against aphids were required in the first year. During both years weeds were hand removed when necessary. At flowering all the heads of the high oleic hybrid were protected with nylon mesh to avoid cross pollination by insects, but that allowed the passage of air and water so as to avoid forming a specific microclimate around the head that would interfere with the biochemical and physiological activity of the forming achenes. The high self-compatibility of the genotype allowed full fertilisation of the flowers. The experimental layout was a randomised block design, with 1 genotype (UD12), 3 irrigation treatments (restoration of 60% of ETM, 50 cm deep water table and stress) and 4 replicates in the first year and 2 genotypes (UD12 and UD87), 3 irrigation treatments (restoration of Fatty Acids in Sunflower Hybrids 121 Table 2. Treatments adopted and analysed characters on sunflower hybrids at harvest time. Means with same letters are not significantly different P ≤ 0.05 (Duncan test). (1) 60 and 100% ET= restoration of 60 and 100% of ETM; Table 0.5 and 0.6 m= water table depth; Stress= no water restoration from flowering to physiological maturity. Year Hybrids Water regime (1) Achene yield Single achene Achenes per Oil content (g m -2 ) weight (mg) plant (n°) (% s.s.) 1997 High oleic 60% ET 328 b 42.3 ac 1033 b 45.5 ab “ “ Table 0.5 m 512 a 45.2 ac 1510 a 43.5 ab “ “ Stress 144 c 25.8 bc 2743 c 42.2 ab 1998 High oleic 100% ET 513 a 48.3 ac 1326 b 40.9 bb “ “ Table 0.6 m 540 a 46.5 ac 1453 a 47.2 ab “ “ Stress 304 c 40.6 bc 2936 c 43.5 ab “ Standard 100% ET 493 ab 43.5 ab 1416 a 39.4 bb “ “ Table 0.6 m 432 b 44.6 ab 1210 b 45.9 ab “ “ Stress 235 d 39.9 bc 2737 d 42.8 ab 100% of ETM, 60 cm deep water table and stress) and 4 replicates, in the second. At harvest, the achenes, after oven drying (72 hours at 50 °C), were used for the following determinations: − achene production per unit surface area (g m -2 ); − achene unit weight (mg); − filled achenes per plant (n); − oil content in the achenes (% of dry weight), using the NMR (Nuclear Magnetic Resonance) method. Six samples of 10 achenes were taken from each treatment starting at 5 days from the end of flowering, stage F4 (Merrien, 1986), until maturity, stage M3 (Merrien, 1986). The samples were taken from four plants (one plant per lysimeter in the first year and two plants in the second, respectively), always from the external zone of the head. The achenes were immediately ovendried (72 hours at 60 °C) and stored in a cold room (4 °C) until the end of the trial. On each of these samples the following determinations were made: − whole achene unit weight (in the second year) (mg); − oil content (% of dry weight), following the method used by Champolivier and Merrien (1996) (in the second year), by hexane extraction; − percentage content of the major fatty acids in the oil: stearic acid (C16:0), palmitic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2), using the esterification and gas-chromatography methodology described by Fernandez et al. (1999).
Page 1: Ital. J. Agron., 6, 2, 119-126 Effe
Page 5 and 6: values, by circa 50% in the standar
Page 7 and 8: presence and complete ETM restorati

¥Agronomia vol. 6 n. 2 July

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